1. Field of the Invention
The invention is concerned with a vehicle-retarding engine braking system of the compression relief type. In particular, the invention relates to a braking system of the compression relief type which is employed in engines of vehicles to aid in slowing down the vehicle in normal operation by opening an exhaust valve or valves to relieve the related cylinder or cylinder of the gases of compression near the end of a compression stroke or stroke. In effect, one, more or all of the cylinders of the engine are converted from power-producing engine components into a power-absorbing air compressor.
2. The Prior Art
A vehicle-retarding, engine braking system of the compression relief type is known from the U.S. Pat. No. 3,220,392 to Clessie L. Cummins entitled "Vehicle Engine Braking and Fuel Control System" and granted Nov. 30, 1965. When this prior art system is placed into operation, a slave piston is hydraulically operated against a return spring to open an exhaust valve or valves of a cylinder or cylinders in a timely fashion so that the exhaust valve or valves is opened near the end of its compression stroke thereby allowing the gases of compression to escape from the cylinder or cylinders near the end of the compression strokes. It was determined that if the slave piston should fail to return after opening the exhaust valve, for example because of a broken spring or the like, the slave piston may become locked or be jacked downwardly relative to the exhaust valve or valves by hydraulic fluid, preventing the exhaust valve or valves from closing.
The problem of the locked or downwardly jacked exhaust valves was recognized and the problem solved by a modified vehicle-retarding, engine braking system as disclosed in the U.S. Pat. No. 3,405,699 to Laas entitled "Engine Braking System with Trip Valve Controlled Piston" and granted Oct. 15, 1968. The modified system involved replacing the slave piston with a combined safety trip valve and work piston. In an engine braking system of the compression relief type, the combined trip valve and work piston causes the exhaust valve to open at a time other than the normal time and also assures that the work piston does not become locked.
The above-mentioned type vehicle-retarding, compression relief type engine braking systems are generally operatively associated with an arming switch on the dash of the vehicle, where it is accessible to a driver, so that the driver may arm the system, that is, ready the system for operation. Additional switches, generally in electrical series with the arming switch, are operatively positioned to be closed respectively whenever the clutch is engaged, whenever the transmission is in a position other than neutral, and/or whenever the throttle is positioned for a predetermined low engine speed or an idle engine speed or less.
The braking systems of the compression relief type can be combined with other engine braking systems, for example, systems in which combustion in the cylinders is interrupted and/or systems in which back pressure is created in the exhaust manifold. A vehicle retarding engine braking arrangement which combines all three types of systems is known from the U.S. Pat. No. 3,525,317 to Earl B. Muir entitled "Vehicle Engine Braking System" and granted Aug. 25, 1970.
Vehicle-retarding, engine braking systems of the compression relief type have come into widespread use on trucks, particularly on large trucks. The systems provide extra retarding power, reduce cost and allow drivers to achieve better vehicle performance and control. One such system, available for the Cummins L10 engine from the Jacobs Manufacturing Company of Bloomfield, Conn. under the designation 404 Jake Brake.RTM. is said to provide as much as 350 retarding horsepower at the drive wheels for efficient slowing and good vehicle control. The probability of a runaway accident has been recognized as being about three times less were a truck equipped with a retarder; see Faucher et al. "Retarders for Heavy Vehicles: Phase II Field Evaluations", DOT HS No. 806 297, June 1982, page 75.
The known above-mentioned vehicle-retarding braking systems of the compression relief type are generally provided with an arming switch which, as noted above, is a manua1ly operated ON-OFF switch positioned on the dashboard of a vehicle. The positioning of the switch on the dashboard, however, has distinct disadvantages because an operator must remove one of his hands from either the steering wheel of the vehicle or from the knob of the shift lever, in the event it is desired to arm the system while the vehicle is in motion. The actual arming is delayed, with possible serious consequences where road, load, weather or other environmental circumstances change while underway. Often, the operator, as well as the vehicle, is put in jeopardy, especially where the operator attempts to reach through the steering wheel to arm the vehicle. On the other hand, the "JAKE BRAKE" is intended for intermittent operation and is not intended to be "armed" continuously, especially in heavy traffic conditions.
Moreover, the prior art systems do not allow an operator to use the arming switch conveniently in such a way to effect intermittent use while the vehicle is being operated on a down-hill grade or the like, especially on slick surfaces.